1. Field of the Invention
The present invention relates to a fiber reinforced inorganic hardened body and a process for its production. More particularly, it relates to an inorganic hardened body, particularly a cement mortar hardened body, reinforced by a fiber reinforcing material, particularly a glass fiber reinforcing material, in a form of a loopy mat wherein a plurality of fiber strands are piled in an irregular loopy fashion, or in a form of a continuous mat or net, and a process for its production.
2. Description of the Prior Art
A glass fiber reinforced cement (hereinafter referred to as "GRC") is known as a typical example of the fiber reinforced inorganic hardened body.
As typical methods for producing the fiber reinforced inorganic hardened body represented by such GRC, there have been known a so-called direct spray method in which cement mortar and glass fibers are simultaneously sprayed by guns onto a mold surface to form a GRC layer, which is then released from the mold to obtain a formed body, and a so-called premix method in which cement mortar premixed with glass fibers is fed into a predetermined mold and molded therein. The former method is suitable for the production of a generally flat thin product. It is thereby possible to maintain a water/cement ratio at a relatively low level, whereby a product having fairly satisfactory strength is obtainable. However, a loss of the materials is substantial, the thickness tends to be uneven, and it is thereby difficult to obtain a smooth flat surface having no substantial defects. Further, the fibers tend to localize, and this fact leads to formation of voids or local concentration of the mortar, and thus weak portions are likely to form, whereby the strength tends to be uneven. Furthermore, the fibers and cement tend to be separated from each other to form a layered structure which is susceptible to separation into layers when a shearing force is exerted thereto. Whereas, according to the latter premix method, the thickness of the product can relatively freely be chosen. However, this method has a disadvantage that the fibers are susceptible to damages when they are mixed with the cement mortar. Further, the fibers tend to be formed into balls. It is further necessary to adjust the water/cement ratio at a relatively high level in order to maintain the flowability, whereby the strength of the formed product tends to be low.
Further, in both of the above mentioned methods, so-called chopped strands having a short length are used as the fiber reinforcing material, and the strength of GRC thereby obtainable is limited to a relatively low level.
On the other hand, there have been several proposals wherein a reinforcing material of a continuous form such as a mat is used as the fiber reinforcing material for production of GRC. However, as opposed to the case of a fiber reinforced polymer (i.e. so-called FRP) where the resin as a constituent of the FRP can adequately penetrate into the fibers irrespective of the form of fibers, the cement mortar in the case of the GRC cannot adquately penetrate into the fibers without influence of the form of the fibers. Accordingly, when the above mentioned reinforcing material of a continuous form such as a mat is used, the product will have portions where no cement mortar or no adequate amount of cement mortar is present. In an attempt to overcome this difficulty, it has been proposed to give vibrations during the forming step. However, such an attempt has been found to be not so effective. There has been no proposal for a fully satisfactory forming means.